The nitration of aromatic hydrocarbons, and, in particular, of benzene and toluene, is normally carried out on a commercial scale by reacting the aromatic hydrocarbon with a mixture of nitric and sulfuric acids under controlled temperature. This mixed acid process suffers from the use of large volumes of the highly corrosive mixture of nitric and sulfuric acids and the formation of by-products including the highly undesirable and potentially explosive polynitrated hydrocarbons.
Various methods for nitrating aromatic hydrocarbons without the use of a mixed acid are known:
U.S. Pat. No. 1,325,168 describes passing an oxidizing agent, such as oxygen, into a mixture of an aromatic hydrocarbon and liquid nitrogen peroxide.
U.S. Pat. No. 2,109,873 describes passing a gaseous mixture of an aromatic hydrocarbon and nitrogen dioxide through a bed of silica gel to obtain the mononitro derivative of the aromatic hydrocarbon.
U.S. Pat. No. 2,431,585 describes the vapor phase nitration of an aromatic hydrocarbon to produce the mononitro derivative using nitrogen dioxide and a catalyst which is selected from metal metaphosphate, boron phosphate, solid and supported phosphoric acid.
U.S. Pat. No. 3,459,816 describes nitrating a dialkylbenzene with dinitrogen tetroxide in a halogenated hydrocarbon solvent at a temperature of about 90.degree. to 160.degree. C. to effect substitution of the nitro group on the alkyl substituent.
U.S. Pat. No. 3,856,859 discloses the position-selective nitration of alkanesulfonanilides using an equimolar amount of a nitrating agent, such as dinitrogen tetroxide in chloroform or trifluoroacetic acid.
U.S. Pat. No. 3,922,315 describes a process for the mononitration of aromatic compounds by contacting the aromatic compound with nitrogen dioxide and/or its dimer, nitrogen tetroxide, in the presence of a rhodium catalyst and hydrogen.
U.S. Pat. No. 3,929,917 discloses a process for mononitrating ortho-xylene by reacting the ortho-xylene with nitrogen tetroxide (N.sub.2 O.sub.4) or nitrogen dioxide (NO.sub.2) and an oxygen containing gas in the presence of a mercuric salt dissolved in acetic acid at temperatures above about 20.degree. C.
U.S. Pat. No. 4,028,425 describes a continuous process for the concurrent production of dinitrotoluene and nitric acid by continuously introducing toluene, nitrogen dioxide or nitrogen tetroxide and oxygen in specified molar ratios into a reaction zone containing a reaction medium comprising dinitrotoluene and 93-103% nitric acid.
U.S. Pat. No. 4,104,145 describes the nitration of benzene by the use of nitrogen dioxide under irradiation of visible ray or ultra violet ray in the presence of oxygen.
U.S. Pat. No. 4,123,466 describes reacting an aromatic hydrocarbon with gaseous nitrogen dioxide in the presence of a catalytic amount of sulfuric acid and in the absence of oxygen.
D. S. Ross and W. G. Blucher, "A Novel Nitration System," 174th meeting of Am. Chem. Soc., Chicago, Ill., August 1977, disclosed the production of nitrobenzenes by dissolving benzene and nitric oxide (NO) in liquid N.sub.2 O.sub.4 at 0.degree. C. under 2 atmospheres oxygen.